Pro Series II 2.5" Tubes - Supersonic?

[Rocketholic]

Hey all,

I'm working on scratch building a 43" tall semi-scale rocket using PS II 2.5" tubes, G10 FG fins, and a 38mm motor mount with 29mm adapter. Non-glassed w/o motor: ~23 oz. I don't want to disclose more details at this time but if all goes well, I'll put up a thread about it. This will likely be my L1 cert rocket.

So, my question stems from sim'ing higher power 38mm motors with OR and seeing that some I & J-class motors will send it supersonic and over 5k ft. Can PS II tubes handle 40+ G's and supersonic flight? Anyone come close to testing them at these extremes?

An Aerotech H100W (pretty mild thrust curve) will send at 1/2 the sos to 2900 ft pulling only 13.5 G's. An HP J270T will pretty much double everything. An HP I500... don't even think about it!

Once I saw some of the G's reaching tennis ball flattening levels and velocities in excess of 1200 fps I started considering glassing the body. PS II tubes are pretty stout, but any small failure would lead to a catastrophic premature and likely violent disassembly.

Thoughts?

 

[David_Stack]

Partizon with an I-something... (no glass if I recall)

https://www.rocketryforum.com/threads/loc-vulcanite-vs-estes-partizon-build-challenge.66012/

 

[SolarYellow]

The 2.5-inch tube is 0.035 inch wall thickness, as opposed to 0.040-inch thickness on the standard HPR "2.6 inch" tubes. You're not giving up much, and getting a lighter nose cone if you use the Estes part.

https://www.rocketryforum.com/threa...zon-build-challenge.66012/page-4#post-1469894

 

[Art Upton]

I flew my 2.5" PSII Partizon on an I205 twice , going about 1 mile high on the stock fins. Internal fillets to the motor tube only, slots only sealed on the body tube.

As I was shipping the rocket the tubes were only masking tape tight on the couplers for the fight. They were not glued together so I could separate them and put them back in the shipping box. I still have that rocket.

 

[Rocketholic]

Thank you all for your responses. I did do a quick search for PS II tubes but came up dry so made this thread. I see now that the PS II 2.5" tubes can handle a fair amount without issue. This is great news! I won't have to bother with glassing the rocket.

Thanks again!

 

[David_Stack]

You mentioned "J" motors in your initial post, I would shy away from those, and build a dedicated rocket for your L2 certification. Just something to think about...

 

[lr64]

Why do people make solid G10 fins? Is it because their rockets would be too light, nose heavy, and stiff without them? Cored or built up structures that are somewhat thicker will show superior strength and stiffness at lighter weights. And superior flutter resistance. For sure when subsonic. I don't know just how thin one is forced to go for efficiency when supersonic, but of course if you want efficiency, you will end up at higher altitudes.

Whether a PSII can handle 40 g's will depend in part on how heavy it's contents, and particularly the nose cone and any nose weight are.

I don't know what kind of resin they use with that stuff, so I have no idea how stiff or strong it is. I do know that, for equivalent weights rather than thicknesses, the bending stiffness to weight ratio of epoxy saturated kraft paper is comparable to that of epoxy with fiberglass cloth. Thin walled tube of equal weight, general design, and external size made of these materials would buckle at similar loads if the wall thickness is adjusted for equal weight.

 

[SolarYellow]

Why do people make solid G10 fins? Is it because their rockets would be too light, nose heavy, and stiff without them? Cored or built up structures that are somewhat thicker will show superior strength and stiffness at lighter weights. And superior flutter resistance. For sure when subsonic. I don't know just how thin one is forced to go for efficiency when supersonic, but of course if you want efficiency, you will end up at higher altitudes.

G10 sheet is reliably much flatter than any source I've found for plywood, balsa, or bass, so you can order online and know you'll get something you can work with instead of having to go to a brick and mortar store and sort through their stock looking for pieces you want to make fins out of, or ordering online and ending up with a lifetime supply of centering ring/ebay stock instead of the fin stock you wanted. G10 sheet is significantly cheaper than carbon fiber sheet. Cutting fins out of a G10 sheet is easier and faster than glassing and bagging a wood or other core, and it takes less work to make the G10 sheet smooth and ready for paint.

For lots of rockets, G10 is more than good enough and the efficient way to get it done. If you have electronics in the nose and/or an airframe longer than it needs to be, as most HPR designs are, you're probably not hurting for stability. Typical HPR rockets aimed at high apogee tend to come out below optimum weight anyway, so adding a little more nose weight to keep things balanced actually helps them go higher.

Are there realms where I'd rather have carbon fiber or would build up the fins using composite structures? Sure. But just because you can doesn't mean you have to or that it's necessary or the best solution for every circumstance.

 

[Rocketholic]

You mentioned "J" motors in your initial post, I would shy away from those, and build a dedicated rocket for your L2 certification. Just something to think about...

I wasn't even considering using a J-class motor. Yes, I mentioned it but only as a data point. I suppose if I wanted to test the rocket and the electronics inside on a likely one-way flight then perhaps. But nah, I'm having too much fun with the design/build to send it like that.
I bought the nose cone on sale and needed to build a rocket to put it on and decided on something that would suit it well and that I really liked.

I appreciate your concern and advice. I have accumulated some great materials to build an L2 rocket from - big, strong, and not very light.

 

[Rocketholic]

G10 sheet is reliably much flatter than any source I've found for plywood, balsa, or bass, so you can order online and know you'll get something you can work with instead of having to go to a brick and mortar store and sort through their stock looking for pieces you want to make fins out of, or ordering online and ending up with a lifetime supply of centering ring/ebay stock instead of the fin stock you wanted. G10 sheet significantly cheaper than carbon fiber sheet. Cutting fins out of a G10 sheet is easier and faster than glassing and bagging a wood or other core, and it takes less work to make the G10 sheet smooth and ready for paint.

For lots of rockets, G10 is more than good enough and the efficient way to get it done. If you have electronics in the nose and/or an airframe longer than it needs to be, as most HPR designs are, you're probably not hurting for stability. Typical HPR rockets aimed at high apogee tend to come out below optimum weight anyway, so adding a little more nose weight to keep things balanced actually helps them go higher.

Are there realms where I'd rather have carbon fiber or would build up the fins using composite structures? Sure. But just because you can doesn't mean you have to or that it's necessary or the best solution for every circumstance.

Thank you. I was thinking along the same lines. I have a stack of lite-ply that could have been up to the task but I wanted to try something different. I also wanted to avoid having to sort through the bows and warps to find the right pieces.
I'm only using 1/16" (1.5mm) thick FG to help with the weight issue. Even at that thickness it is surprisingly rigid. I didn't put a mic or calipers on it but looks closer to 2mm. 1/8-3/16" ply vs 1/16" FG is almost a wash weight-wise. Cutting 12 fins on my benchtop scroll saw was a chore but sanding was quick and easy on the belt sander. The dust is not pleasant and to be avoided!

The tiny amount of extra weight of the aft sets of fins helped balance the weight of the electronics in the nose. The deployment vehicles are also forward of the midpoint. Balancing should be rather easy.

I fully design my models in OR using dimensions and weights as accurate as I can get them before the build starts.

 

[SolarYellow]

This is the way to cut G10 or carbon fiber plate:

https://www.lowes.com/pd/SKIL-7-in-4-2-Amp-Wet-Tabletop-Tile-Saw/5005413927

If you have a Lowe's cc, that's 5% off.

Hazard Fraught has a knockoff, but that doesn't include a blade, so it's actually more expensive by the time you get up and cutting. It will be messy with the water, but at least the material isn't in the air or my lungs.

I'm waiting to see what happens on Prime Day with that and a few other larger tool purchases.

 

[lr64]

Regular wood is probably a lot better than G10, at the same weight, and some kinds of plywood tend to be pretty flat. Thin plywood over foam or balsa would be even better, assuming the foil can be thick enough. On something this small, I wouldn't be surprised if plain balsa was superior. Much stiffer for the weight, anyway. You might have to leave the trailing edge a bit wider, and maybe have a strip of harder wood there for landing loads.